A capacitor is a passive two-terminal electrical component used to store energy electrostatically in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors (plates) separated by a dielectric (i.e., insulator). The conductors can be thin films of metal, aluminum foil or disks, etc. The ‘nonconducting’ dielectric acts to increase the capacitor's charge capacity. A dielectric can be glass, ceramic, plastic film, air, paper, mica, etc. Capacitors are widely used as parts of electrical circuits in many common electrical devices and function to store energy in the form of an electrostatic field between its plates.
A capacitor has two sets of connection features: electrical and mechanical. The mechanical set is intended to be a rigid connection to some structure to support the mechanical load due to the mass of the capacitor. The electrical set is intended to be a strictly electrical connection that supports no mechanical load other than that due to the clamping of electrical terminals of the capacitor to an electrically conductive structure. This type of coupled connection is practical when the conductor attached to the capacitor's electrical terminals is mechanically compliant or readily deformable, such as wires or cables or a thin layer of copper.
Complex systems can require numerous capacitors and other components to which the capacitors are connected in the circuit of the system and to which cables must be run to and from the capacitors. In systems with high electrical currents, the size of cables can be large which makes assembly of the wires difficult, time consuming, and inefficient in its use of available packaging space. The same concerns apply to layers of copper, which can also require separate electrical insulation layers to be installed in the assembly.
A laminated busbar can be used to make efficient use of the available space and improve upon the assembly time required for cables or individual layers of copper and insulation. It also offers an improvement in inductance when compared with equivalent cabling. However, a laminated busbar with multiple layers is stiff in comparison to the previous conductors. This stiffness introduces a rigid connection in two different planes for the capacitors. Any variation from the nominal dimensions of the capacitor geometry may introduce added assembly stresses to both the electrical and mechanical connections. An electrical joint that is both free of mechanical stress and is a rigid non-compliant connection between the capacitor and busbar is therefore desirable to maximize reliability and durability of the system over time.
For example, with reference to FIG. 1, a typical capacitor assembly 10 consists of a plurality of capacitors 12, 14, 16, each having a mounting foot 18 and a pair of electrical terminals 20 operatively attached to a laminated busbar 22 in a mounting plane 24 necessary for electrical contact. As will be readily appreciated, capacitors are designed to a nominal height, however, normal manufacturing variations and accepted manufacturing tolerances result in the production of capacitors that are both taller and shorter than this nominal value. For example, as shown in FIG. 1, first capacitor 12 may have the desired, nominal height. A second capacitor 14, however, may have a larger height and a third capacitor 16 may have a smaller height, but still within manufacturing tolerances. As noted above, it is desirable that the electrical terminals 20 of each of the capacitors 12, 14, 16 connect to the laminated busbar 22 with minimal mechanical stress, while the mass of the capacitors 12, 14, 16 is supported by attaching the mounting feet 18 to some support structure via fastening means known in the art. As will be readily appreciated, the variation in height either requires each capacitor to connect to the busbar 22 in a separate plane, or to the support structure in a separate plane, while maintaining electrical contact with the laminated busbar 22 with minimal mechanical stress and with the mass of the capacitors being supported at each mounting foot 16.
As illustrated in FIGS. 2 and 3, if the distance between the laminated busbar 22 and support structure 26 is rigid and is designed to match the nominal height of the busbar 22, mechanical stress is introduced as the busbar 22 and/or support 26 deflects to accommodate the height variation. For example, as shown in FIG. 2, mechanical stress may be introduced into the support structure 26 at 28 due to the height variation of the tallest capacitor 14, and at 30 due to the height variation of the shortest capacitor 16. As shown in FIG. 3, mechanical stress may also, or alternately, be introduced into the busbar 22 at 32 due to the height variation of the tallest capacitor 14, and at 34 due to the height variation of the shortest capacitor 16. Undesirably, this mechanical stress introduced in the support structure 26 and/or busbar 22 can translate to undesirable stress on the electrical terminals 18 of the capacitors.